Ferdi is an will forever be completely free! There are no hidden fees, paywalls or subscriptions.
One of our main reasons for creating Ferdi was that Franz started to lock more and more features behind paywalls without offering any new features for free users. Ferdi has removed all paywalls and all new features will be available for all users.
Please do however keep in mind that we still have to pay bills to keep Ferdi's infratructure up and running (Servers, licenses etc.). So if you are satisfied with Ferdi and want to give something back, please consider donating or sponsoring Ferdi at https://opencollective.com/getferdi.